A smart key system is known, including a portable electronic key and a control device capable of wirelessly communicating with the electronic key. The smart key system controls unlocking and locking of doors as well as starting and stopping of an engine through wireless communications (an authenticating process) carried out between the electronic key and the control device. See, for example, Japanese Laid-Open Patent Publication No. 2003-278629 (hereinafter referred to as “JP2003-278629A”).
According to JP2003-278629A, it is judged whether or not a vehicle is traveling based on a vehicle information signal representative of vehicle speed information or the like. If the vehicle is traveling, then a switch (19) for controlling starting/stopping (on/off) of an engine is inhibited from being pressed, and a pressing operation signal from the switch is invalidated, so that a process will not be performed based on pressing of the switch (see paragraphs [0023], [0024], [0039]).